Fix detection of IBM Power8 machines (ISA 2.07)

An IBM POWER7 system with Power ISA 2.06 tried to execute
zfs_sha256_power8() - which should only be run on ISA 2.07
machines.

The detection is implemented via the zfs_isa207_available() call,
but this check was not used.

This pull request will fix this.

Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>

module/icp/algs/sha2/sha256_impl.c

@@ -141,9 +141,9 @@ const sha256_ops_t sha256_armv8_impl = {
 };
 
 #elif defined(__PPC64__)
-static boolean_t sha256_have_vsx(void)
+static boolean_t sha256_have_isa207(void)
 {
-	return (kfpu_allowed() && zfs_vsx_available());
+	return (kfpu_allowed() && zfs_isa207_available());
 }
 
 TF(zfs_sha256_ppc, tf_sha256_ppc);
@@ -155,7 +155,7 @@ const sha256_ops_t sha256_ppc_impl = {
 
 TF(zfs_sha256_power8, tf_sha256_power8);
 const sha256_ops_t sha256_power8_impl = {
-	.is_supported = sha256_have_vsx,
+	.is_supported = sha256_have_isa207,
 	.transform = tf_sha256_power8,
 	.name = "power8"
 };